Adult Human Vein Grafts Retain Plasticity of Vessel Identity

Disturbed flow in the juxta-anastomotic area of an arteriovenous fistula correlates with endothelial loss, acute thrombus formation, and neointimal hyperplasia

Clinical failure of arteriovenous neointimal hyperplasia (NIH) fistulae (AVF) is frequently due to juxta-anastomotic NIH (JANIH). Although the mouse AVF model recapitulates human AVF maturation, previous studies focused on the outflow vein distal to the anastomosis. We hypothesized that the juxta-anastomotic area (JAA) has increased NIH compared with the outflow vein. AVF was created in C57BL/6 mice without or with chronic kidney disease (CKD). Temporal and spatial changes of the JAA were examined using histology and immunofluorescence. Computational techniques were used to model the AVF. RNA-seq and bioinformatic analyses were performed to compare the JAA with the outflow vein. The jugular vein to carotid artery AVF model was created in Wistar rats. The neointima in the JAA shows increased volume compared with the outflow vein. Computational modeling shows an increased volume of disturbed flow at the JAA compared with the outflow vein. Endothelial cells are immediately lost from the wall contralateral to the fistula exit, followed by thrombus formation and JANIH. Gene Ontology (GO) enrichment analysis of the 1,862 differentially expressed genes (DEG) between the JANIH and the outflow vein identified 525 overexpressed genes. The rat jugular vein to carotid artery AVF showed changes similar to the mouse AVF. Disturbed flow through the JAA correlates with rapid endothelial cell loss, thrombus formation, and JANIH; late endothelialization of the JAA channel correlates with late AVF patency. Early thrombus formation in the JAA may influence the later development of JANIH.NEW & NOTEWORTHY Disturbed flow and focal endothelial cell loss in the juxta-anastomotic area of the mouse AVF colocalizes with acute thrombus formation followed by late neointimal hyperplasia. Differential flow patterns between the juxta-anastomotic area and the outflow vein correlate with differential expression of genes regulating coagulation, proliferation, collagen metabolism, and the immune response. The rat jugular vein to carotid artery AVF model shows changes similar to the mouse AVF model.

Delivery of rivaroxaban and chitosan rapamycin microparticle with dual antithrombosis and antiproliferation functions inhibits venous neointimal hyperplasia

Neointimal hyperplasia is a complex process after vascular interventions, acute platelet deposition and smooth muscle cell proliferation both contributed to this process. There are still no perfect solutions to solve this problem. Rivaroxaban is a novel anticoagulant that has been widely used in clinic, it has a good pharmacological effects both in vivo and in vitro. Chitosan microparticle rapamycin (MP-rapa) was fabricated, interspaces of polyglycolic acid (PGA) scaffold were used as a reservoir of MP-rapa, and the scaffold was coated with hyaluronic acid rivaroxaban (MP-rapa-riva). Scanning electronic microscopy (SEM) photographs were taken and water contact angles were measured, rat inferior vena cava (IVC) patch venoplasty model was used; patches were harvested at day 14 and examined by immunohistochemistry and immunofluorescence. SEM photographs showed the microparticles rapamycin were inside the interspace of the scaffold, hyaluronic acid rivaroxaban was also successfully coated onto the surface of the scaffold. There was a thinner neointima, fewer proliferating cell nuclear antigen (PCNA) positive cells, fewer macrophages in the MP-rapa and MP-rapa-riva grafts compared to the control PGA graft. The result showed that this scaffold with dual anticoagulation and antiproliferation functions can effectively inhibit venous neointimal hyperplasia, although this is an animal experiment, it showed promising potential clinical application in the future.

A Novel Plant Leaf Patch Absorbed With IL-33 Antibody Decreases Venous Neointimal hyperplasia

Introduction: We recently showed that a decellularized leaf scaffold can be loaded with polylactic-co-glycolic acid (PLGA)-based rapamycin nanoparticles, this leaf patch can then inhibit venous neointimal hyperplasia in a rat inferior vena cava (IVC) venoplasty model. IL-33 plays a role in the neointimal formation after vascular injury. We hypothesized that plant leaves can absorb therapeutic drug solution and can be used as a patch with drug delivery capability, and plant leaves absorbed with IL-33 antibody can decrease venous neointimal hyperplasia in the rat IVC venoplasty model. Method: A human spiral saphenous vein (SVG) graft implanted in the popliteal vein was harvested from a patient with trauma and analyzed by immunofluorescence. Male Sprague-Dawley rats (aged 6-8 weeks) were used to create the IVC patch venoplasty model. Plant leaves absorbed with rhodamine, distilled water (control), rapamycin, IL-33, and IL-33 antibody were cut into patches (3 × 1.5 mm²) and implanted into the rat IVC. Patches were explanted at day 14 for analysis. Result: At day 14, in the patch absorbed with rhodamine group, immunofluorescence showed rhodamine fluorescence in the neointima, inside the patch, and in the adventitia. There was a significantly thinner neointima in the plant patch absorbed with rapamycin (p = 0.0231) compared to the patch absorbed with distilled water. There was a significantly large number of IL-33 (p = 0.006) and IL-1β (p = 0.012) positive cells in the human SVG neointima compared to the human great saphenous vein. In rats, there was a significantly thinner neointima, a smaller number of IL-33 (p = 0.0006) and IL-1β (p = 0.0008) positive cells in the IL-33 antibody-absorbed patch group compared to the IL-33-absorbed patch group. Conclusion: We found that the natural absorption capability of plant leaves means they can absorb drug solution efficiently and can also be used as a novel drug delivery system and venous patch. IL-33 plays a role in venous neointimal hyperplasia both in humans and rats; neutralization of IL-33 by IL-33 antibody can be a therapeutic method to decrease venous neointimal hyperplasia.

Early Outcomes of Complex Vascular Reconstructions in Lower Extremities Using Spiral and Panel Vein Grafts

BACKGROUND

Spiral saphenous vein grafts (SSVG) or paneled vein grafts (PVG) can be used when the diameter of the autologous great saphenous vein does not match the vessel that needs to be repaired. This study aimed to present early results of complex vascular reconstruction with SSVGs and PVGs in the lower extremities.

METHODS

From May 2019 through January 2021, 6 SSVGs and 3 PVGs were used for vascular reconstruction in 9 patients. Patient data were collected retrospectively, including age, gender, cause of vascular pathology, target vessels, concomitant injury, surgical method, additional surgical methods, and hemodynamic status. The Kaplan-Meier method was used to calculate the rate of freedom from reintervention.

RESULTS

Among these patients, 7 had trauma, 1 had graft infection, and 1 had vascular reconstruction after tumor excision. The mean duration of follow-up was 6 ± 6.6 months (range 1-19 months). The rate of freedom from reintervention for any reason was 77.8% at 1 year. Two patients underwent amputation after vascular reconstruction with patent vascular reconstructions. One of the 2 amputations was performed because of infection, and the other was due to ischemia >24 hr. The success rate of reconstruction was 100%, and the primary patency rate was 100%. The rate of limb salvage was 77.8%. There was no death, bleeding, embolism, skin ulcers, graft-related complication, or aneurysmal dilation during follow-up.

CONCLUSIONS

SSVG and PVG were associated with low infection rates and satisfactory short-term patency rates. Both 2 grafts may be good choices when there is a diameter mismatch in vascular reconstructions.

Biomimetic Elastin Fiber Patch in Rat Aorta Angioplasty

Introduction: Vascular grafts significantly contribute to advances in vascular surgery, but none of the currently available prosthetic grafts have elastin fibers similar to native arteries. We hypothesized that a novel elastin patch could be produced after a rat decellularized thoracic aorta elastin fiber scaffold is implanted subcutaneously in rats; we tested this novel elastin patch in a rat aortic arterioplasty model. Methods: Sprague-Dawley rats (200 g) were used. Rat thoracic aortae were decellularized and sectioned at a thickness of 30 μm. A single elastin fiber scaffold was fabricated as a net (5 × 5 mm²), and then a three-layer scaffold was constructed to make a new patch. The hyaluronic acid-sodium alginate (HA/SA) hydrogel was fabricated by reacting sodium SA, HA, and CaCO₃, and then the hydrogel was added to the patch to secure the elastin fibers. The patches were implanted subcutaneously in rats and harvested at day 14. The elastin patches were then implanted into the same rat's aorta and harvested at day 14; a decellularized rat thoracic aorta (TA) patch was used as a control. Sections of the retrieved patches were stained by immunohistochemistry and immunofluorescence. Results: The elastin fibers could be secured by the hydrogel. After 14 days, the subcutaneously implanted elastin patch was incorporated into the rat tissue, and H&E staining showed that new tissue had formed around the elastin patch with almost no hydrogel left. After implantation into the rat aorta and then retrieval on day 14, H&E staining showed that there was neointima and adventitia formation in both the TA and elastin patch groups. Both patches showed a similar histological structure after implantation, and immunofluorescence showed that there were CD34- and nestin-positive cells in the neointima. In both groups, the endothelial cells expressed the arterial identity markers Ephrin-B2 and dll-4; almost one-third of the cells in the neointima were PCNA-positive with rare cleaved caspase-3-positive cells. Conclusion: We demonstrated a novel approach to making elastin fiber scaffold hydrogel patches (elastin patches) and tested them in a rat aorta arterioplasty model. This patch showed a similar healing process as the decellularized TA patch; it also showed potential applications in large animals and may be a substitute for prosthetic grafts in vascular surgery.

The application of tissue-engineered fish swim bladder vascular graft

Small diameter (< 6 mm) prosthetic vascular grafts continue to show very low long-term patency, but bioengineered vascular grafts show promising results in preclinical experiments. To assess a new scaffold source, we tested the use of decellularized fish swim bladder as a vascular patch and tube in rats. Fresh goldfish (Carassius auratus) swim bladder was decellularized, coated with rapamycin and then formed into patches or tubes for implantation in vivo. The rapamycin-coated patches showed decreased neointimal thickness in both the aorta and inferior vena cava patch angioplasty models. Rapamycin-coated decellularized swim bladder tubes implanted into the aorta showed decreased neointimal thickness compared to uncoated tubes, as well as fewer macrophages. These data show that the fish swim bladder can be used as a scaffold source for tissue-engineering vascular patches or vessels.

Bai et al. employ a fish bladder-derived decellularized matrix for the engineering of vascular grafts. The authors show that rapamycin-coated bladder-derived vascular grafts can be implanted as an interposition graft in rats, and that these vascular grafts showed decreased neointimal thickness both in artery and veins.

Programmed death-1 mediates venous neointimal hyperplasia in humans and rats

Venous neointimal hyperplasia can be a problem after vein interventions. We hypothesized that inhibiting programmed death-1 (PD-1) can decrease venous neointimal hyperplasia in a rat inferior vena cava (IVC) patch venoplasty model. The rats were divided into four groups: the control group was only decellularized without other special treatment; the PD-1 group was injected with a single dose of humanized PD-1 antibody (4 mg/kg); the PD-1 antibody coated patches group; the BMS-1 (a PD-1 small molecular inhibitor) coated patches group (PD-1 inhibitor-1). Patches were implanted to the rat IVC and harvested on day 14 and analyzed. Immunohistochemical analysis showed PD-1-positive cells in the neointima in the human samples. There was high protein expression of PD-1 in the neointima in the rat IVC venoplasty model. PD-1 antibody injection can significantly decrease neointimal thickness (p < 0.0001). PD-1 antibody or BMS-1 was successfully conjugated to the decellularized rat thoracic artery patch by hyaluronic acid with altered morphology and reduced the water contact angle (WCA). Patches coated with humanized PD-1 antibody or BMS-1 both can also decrease neointimal hyperplasia and inflammatory cells infiltration. PD-1-positive cells are present in venous neointima in both human and rat samples. Inhibition of the PD-1 pathway may be a promising therapeutic strategy to inhibit venous neointimal hyperplasia.

Accelerated and Improved Vascular Maturity after Transplantation of Testicular Tissue in Hydrogels Supplemented with VEGF- and PDGF-Loaded Nanoparticles

Avascular transplantation of frozen-thawed testicular tissue fragments represents a potential future technique for fertility restoration in boys with cancer. A significant loss of spermatogonia was observed in xeno-transplants of human tissue most likely due to the hypoxic period before revascularization. To reduce the effect of hypoxia-reoxygenation injuries, several options have already been explored, like encapsulation in alginate hydrogel and supplementation with nanoparticles delivering a necrosis inhibitor (NECINH) or VEGF. While these approaches improved short-term (5 days) vascular surfaces in grafts, neovessels were not maintained up to 21 days; i.e., the time needed for achieving vessel stabilization. To better support tissue grafts, nanoparticles loaded with VEGF, PDGF and NECINH were developed. Testicular tissue fragments from 4-5-week-old mice were encapsulated in calcium-alginate hydrogels, either non-supplemented (control) or supplemented with drug-loaded nanoparticles (VEGF-nanoparticles; VEGF-nanoparticles + PDGF-nanoparticles; NECINH-nanoparticles; VEGF-nanoparticles + NECINH-nanoparticles; and VEGF-nanoparticles + PDGF-nanoparticles + NECINH-nanoparticles) before auto-transplantation. Grafts were recovered after 5 or 21 days for analyses of tissue integrity (hematoxylin-eosin staining), spermatogonial survival (immuno-histo-chemistry for promyelocytic leukemia zinc finger) and vascularization (immuno-histo-chemistry for α-smooth muscle actin and CD-31). Our results showed that a combination of VEGF and PDGF nanoparticles increased vascular maturity and induced a faster maturation of vascular structures in grafts.

To be or not to be: endothelial cell plasticity in development, repair, and disease

Endothelial cells display an extraordinary plasticity both during development and throughout adult life. During early development, endothelial cells assume arterial, venous, or lymphatic identity, while selected endothelial cells undergo additional fate changes to become hematopoietic progenitor, cardiac valve, and other cell types. Adult endothelial cells are some of the longest-lived cells in the body and their participation as stable components of the vascular wall is critical for the proper function of both the circulatory and lymphatic systems, yet these cells also display a remarkable capacity to undergo changes in their differentiated identity during injury, disease, and even normal physiological changes in the vasculature. Here, we discuss how endothelial cells become specified during development as arterial, venous, or lymphatic endothelial cells or convert into hematopoietic stem and progenitor cells or cardiac valve cells. We compare findings from in vitro and in vivo studies with a focus on the zebrafish as a valuable model for exploring the signaling pathways and environmental cues that drive these transitions. We also discuss how endothelial plasticity can aid in revascularization and repair of tissue after damage- but may have detrimental consequences under disease conditions. By better understanding endothelial plasticity and the mechanisms underlying endothelial fate transitions, we can begin to explore new therapeutic avenues.